1. Field of the Invention
The invention relates to containers allowing a steady and predetermined loss of heat from within. More specifically, the invention relates to containers for the incubation of yogurt and also to a method of making yogurt.
2. Description of the Prior Art
Centuries ago yogurt was manufactured by placing a bowl of yogurt mixture along side a cooking hearth and the yogurt developed over a period of days. The bowl would get hot enough for yogurt development only when the fire was hot, and cooling took place naturally as the fire died. This cooling period is recognized as the critical period in yogurt development for mild flavor and pleasing texture.
A variety of commercially manufactured yogurt makers are known, typically being powered by electricity for holding the mixture at a predetermined temperature. It is commonly recommended that the yogurt be incubated at a constant heat of about 110.degree.-115.degree. F. for a period of ten hours, at which time the yogurt must be removed from the constant heat yogurt maker. If not removed, the yogurt will cook into separate curds and whey. Other devices, including the Savary device to be described shortly, attempt to speed the yogurt incubation period by holding the mixture at a high temperature for prolonged time. Such rapid processing techniques characteristically produce yogurt having a sharp flavor.
A number of containers in the prior art use insulated walls to preserve heat without the addition of electrically powered heating means. Such containers include a variety of insulated storage bottles and beverage cups, but such containers have the single function of keeping their contents at a temperature as close to their original temperature when placed in the container as possible. Also, U.S. Pat. No. 2,052,253 to Savary sought to achieve non-electrically powered yogurt incubation, but required a rather elaborate system of polished metal walls for heat reflection. In addition, the Savary device, like many electric yogurt makers, attempted to speed the yogurt making process to less than the nine hours needed for a pleasing product, and could overcook the yogurt if left untended.